Synergistic analytical preconcentration with ionic liquid–nanomaterial hybrids

Analytical Chemistry: Tasks, Resolutions and Future Standpoints of the Quantitative Analyses of Environmental Complex Sample Matrices

Currently, the challenges that analytical chemistry has to face are ever greater and more complex both from the point of view of the selectivity of analytical methods and their sensitivity. This is especially true in quantitative analysis, where various methods must include the development and validation of new materials, strategies, and procedures to meet the growing need for rapid, sensitive, selective, and green methods. In this context, given the International Guidelines, which over time, are updated and which set up increasingly stringent “limits”, constant innovation is required both in the pre-treatment procedures and in the instrumental configurations to obtain reliable, accurate, and reproducible information. In addition, the environmental field certainly represents the greatest challenge, as analytes are often present at trace and ultra-trace levels. These samples containing analytes at ultra-low concentration levels, therefore, require very labor-intensive sample preparation procedures and involve the high consumption of organic solvents that may not be considered “green”. In the literature, in recent years, there has been a strong development of increasingly high-performing sample preparation techniques, often “solvent-free”, as well as the development of hyphenated instrumental configurations that allow for reaching previously unimaginable levels of sensitivity. This review aims to provide an update of the most recent developments currently in use in sample pre-treatment and instrument configurations in the environmental field, also evaluating the role and future developments of analytical chemistry in light of upcoming challenges and new goals yet to be achieved.

Ultra-sensitive Sb speciation analysis in water samples by magnetic ionic liquid dispersive liquid-liquid microextraction and multivariate optimization

Efficient separation and preconcentration of inorganic Sb species in different water samples were performed in this work by a novel dispersive liquid-liquid microextraction (DLLME) method based on the application of a magnetic ionic liquid (MIL) and electrothermal atomic absorption spectroscopy (ETAAS) detection. The Sb(iii) species was selectively extracted by complexation with ammonium diethyldithiophosphate (DDTP) and 45 μL of the MIL trihexyl(tetradecyl)phosphonium tetrachloroferrate ([P6,6,6,14]FeCl4) as extractant. Subsequently, a magnetic rod was applied for phase separation, introducing it directly into the sample solution, and the MIL phase was then diluted in chloroform. Afterwards, 15 μL of this solution was injected into the graphite furnace of ETAAS for Sb determination. A multivariate study was performed to obtain the optimal extraction conditions. Selective reduction of Sb(v) to Sb(iii) with 1% (w/v) KI before preconcentration was applied for total inorganic Sb determination and Sb(v) concentration was calculated by subtraction. The analytical performance of the method included extraction efficiencies of 98.0% for Sb(iii) and 92.6% for Sb(v), LOD of 0.02 μg L-1 for Sb(iii) and relative standard deviations of 3.1% for Sb(iii) and 3.5% for Sb(v) (at 6 μg L-1 Sb(iii) and Sb(v), n = 10). The calibration linear range was 0.08-20 μg L-1. The results showed that the proposed methodology was highly sensitive and selective for Sb speciation analysis in tap, dam, mineral, wetland, underground, rain and river water samples.

Nanomaterials in speciation analysis of metals and metalloids

Nanomaterials have draw extensive attention from the scientists in recent years mainly due to their unique and attractive thermal, mechanical and electronic properties, as well as high surface to volume ratio and the possibility for surface functionalization. Whereas mono functional nanomaterials providing a single function, the preparation of core/shell nanoparticles allows different properties to be combined in one material. Their properties have been extensively exploited in different extraction techniques to improve the efficiency of separation and preconcentration, analytical selectivity and method reliability. The aim of this paper is to provide an updated revision of the most important features and application of nanomaterials (metallic, silica, polymeric and carbon-based) for solid phase extraction and microextraction techniques in speciation analysis of some metals and metalloids (As, Cr, Sb, Se). Emphasis will be placed on the presentation of the most representative works published in the last five years (2015-2019).

Fundamental Properties of Packing Materials for Liquid Chromatography

The high performance of chemically-modified silica gel packing materials is based on the utilization of pure silica gels. Earlier silica gels used to be made from inorganic silica; however, nowadays, silica gels are made from organic silanes. The surface smoothness and lack of trace metals of new silica gels permits easy surface modifications (chemical reactions) and improves the reproducibility and stability. Sharpening peak symmetry is based on developing better surface modification methods (silylation). Typical examples can be found in the chromatography of amitriptyline for silanol testing and that of quinizarin for trace metal testing. These test compounds were selected and demonstrated sensitive results in the measurement of trace amounts of either silanol or trace metals. Here, we demonstrate the three-dimensional model chemical structures of bonded-phase silica gels with surface electron density for easy understanding of the molecular interaction sites with analytes. Furthermore, a quantitative explanation of hydrophilic and hydrophobic liquid chromatographies was provided. The synthesis methods of superficially porous silica gels and their modified products were introduced.

A soft material for chromium speciation in water samples using a chemiluminescence automatic system

A soft material formed by multiwall carbon nanotubes and 1-butyl-3-methyl imidazolium chloride was used as sorbent material to perform the chromium speciation in natural waters. This soft material was not yet used for the speciation of metals as chromium. Thus, a multicommutated flow system containing a minicolumn packed with the soft material was designed. The procedure was based on the capacity of the sorbent to retain Cr(VI) as Cr₂O₇⁼ and allow to pass Cr(III) through the column. Then, a fully automated flow-batch analysis system was developed to quantify both species using chemiluminescence detection. Thus, Cr(III) was determined as catalyst of the luminol and hydrogen peroxide reaction and Cr(VI) as oxidant of luminol reaction. This represents a new approach because the oxidation of luminol using Cr₂O₇⁼ has not been reported in literature. The variables of the two systems were optimized. The limits of detection were 1.4 μg L^-1 for Cr(VI) and 4.0 μg L^-1 for Cr(III). The precision of the method was 3.8% and 7.0% for Cr(VI) and Cr(III), respectively. The present method was applied to real water samples with recoveries between 95% and 107%. Besides, these results were in accordance with those obtained using inductive coupled plasma-optical emission spectrometry technique.

A lighter-than-water deep eutectic-solvent-based dispersive liquid-phase microextraction method in a U-shaped homemade device

A new microextraction method, termed glass-filter-based dispersive liquid-phase microextraction using a lighter-than-water deep eutectic solvent, was developed for the extraction and preconcentration of different classes of pesticides from fruit juice and vegetable samples.